Summary:
Tricholoma sejunctum group is characterized by 1) a slightly viscid cap that has black to brown radiating fibrils over a yellowish background, 2) whitish notched gills that often become yellow near the margin of the cap or sometimes overall, 3) a stem that is whitish to yellowish, 4) absent veil, 5) a farinaceous odor, and 6) a white spore deposit. Arora(1) says Tricholoma sejunctum is fairly common in Pacific Northwest. Siegel(2) use the name Tricholoma subsejunctum Peck for what they have in California, partly on the ground that the European Tricholoma sejunctum is hardwood-associated, while acknowledging that Tricholoma viridilutescens is a European spruce-associated species that could prove to be the correct name. The current name of Tricholoma subsejunctum in the online Species Fungorum, accessed June 30, 2020 is Melanoleuca (Peck) Murrill, while MycoBank, accessed the same day, lists the two as obligate or homotypic synonyms.

Cap:
3-8(10)cm across, convex to flat or broadly umbonate; yellow or greenish yellow with "dark innate (flattened) fibrils or streaks radiating from the blackish to brown center"; "slightly viscid or tacky when moist, smooth", sometimes with small scales when old, (Arora), 3.5-7.5cm across, convex when young, becoming nearly flat when old, with low to prominent umbo, margin splitting radially when old; virgate [radially streaked] with blackish or very dark brown fibrils over yellow background, the yellow often visible only at margin, overall color dark greenish yellow; "viscid becoming dry, appressed-fibrillose", (Shanks)

Flesh:
white or tinged yellow (Arora), thin; white to watery gray, in stem white and when old watery gray, (Shanks)

Gills:
"fairly close, typically notched"; at first whitish or creamy white, but often becoming yellow near cap margin or occasionally yellowish throughout, (Arora), adnate to sinuate, close, 0.5-1.5cm broad, thin, splitting when old; pale grayish yellow, pale yellow or pastel yellow, (Shanks)

Stem:
5-8(12)cm x 1-2(3)cm, more or less equal or somewhat swollen in lower part, firm; "whitish, but often developing yellowish tints"; smooth, (Arora); 4-9cm x 1-1.5cm, equal or widening downward to slightly bulbous base, solid or hollow; color often uneven, white with yellow areas or pale yellow to yellow overall; dry, silky-fibrillose, (Shanks)

Veil:
absent (Arora)

Odor:
farinaceous (Arora), not distinctive or farinaceous, (Shanks), of mildew or farinaceous (Miller)

Taste:
"often bitter or nauseating, but in some forms mild", (Arora), not distinctive or farinaceous, (Shanks)

Microscopic spores:
spores 5-7 x 4-5.5 microns, elliptic, smooth, [presumably inamyloid], (Arora), spores 5.3-8.2 x 3.8-6.2 microns, broadly elliptic to nearly round, smooth, inamyloid, colorless; basidia 4-spored, 31-41 x 7.2-9.6 microns, clavate; cheilocystidia absent or rare, 20-35 x 7-14 microns, broadly clavate to spheropedunculate, colorless, thin-walled; clamp connections absent, (Shanks)

Spore deposit:
white (Arora)

Notes:
Tricholoma sejunctum group has been reported from BC by Gamiet(2), from ID by Andrew Parker, pers. comm., and from CA by Desjardin(6). Bessette(5) say it is widely distributed in N. America and show photographs from WA, AK, NY, and WV. There are collections at the University of Washington from AK, WA, OR, and MS, collections at the University of British Columbia from BC and PQ, collections at Oregon State University from OR and FL, and a collection from MT at the New York Botanical Garden.

EDIBILITY

not recommended, poisonous at worst, insipid at best, (Arora)